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Guide to Residential Streets and Paths

C&CAA T51

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ide


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Guide to Residential Streets and Paths

Cement and Concrete Association of Australia

G

uide

First published 1997

Second edition February 2004

C&CAA T51

Cement and Concrete Association of Australia 2004

Except where the Copyright Act allows otherwise, no

part of this publication may be reproduced, stored in a

retrieval system in any form or transmitted by any

means without prior permission in writing from the

Cement and Concrete Association of Australia.

The information provided in this publication is intended

for general guidance only and in no way replaces the

services of professional consultants on particular projects.

No liability can therefore be accepted by the Cement

and Concrete Association of Australia for its use.

DESIGN AND LAYOUT Helen Rix Design

ILLUSTRATION TechMedia Publishing Pty Ltd

ISBN 1-877023-11-6


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01 INTRODUCTION 4

02 TERMINOLOGY

2.1 Definitions 5

2.2 Pavement Types 5

03 STREETSCAPE

3.1 Streetscape Design 6

3.2 Decorative Surface Finishes 7

3.3 Traffic Calming 9

04 DESIGN PROCESS

4.1 General 10

4.2 Site Investigation 10

4.3 The Subgrade 10

4.4 The Subbase 10

4.5 Concrete 114.6 Joints 11

05 SITE INVESTIGATION

5.1 General 11

5.2 Soil Investigation 11

5.3 Traffic Estimation 11

5.4 Site Survey 12

06 SUBGRADES

6.1 General 14

6.2 Subgrade Support 146.3 Subgrade Uniformity 15

6.4 Stabilised Subgrades 16

6.5 Subgrade Preparation 16

07 SUBBASES

7.1 General 17

7.2 Subbase Thickness and Width 17

7.3 Unbound Subbases 17

7.4 Bound Subbases 17

7.5 Subbase Construction 18

08 CONCRETE

8.1 General 18

8.2 Strength 188.3 Skid Resistance 19

8.4 Luminance 20

8.5 Durability 21

8.6 Workability 21

8.7 Chemical Admixtures 21

8.8 Construction Practices 21

09 THICKNESS DESIGN

9.1 General 23

9.2 Design Concept 23

9.3 Factors Used 23

9.4 Concrete Shoulders 23

9.5 Determination of Base Thickness 23

9.6 Steel Reinforcement 23

10 JOINTS

10.1 General 27

10.2 Contraction Joints 27

10.3 Construction Joints 29

10.4 Isolation Joints 30

10.5 Expansion Joints 30

10.6 Joint Sealing 30

10.7 Joint Layout 3110.8 Setting out of Joints 31

11 BIKEWAYS AND FOOTPATHS

11.1 General 35

11.2 Bikeway Pavement Design 36

11.3 Bikeway Construction 37

11.4 Footpaths 38

11.5 Slip Resistance of Concrete

Surfaces 40

11.6 Kerb and Channels 41

11.7 Thresholds 4211.8 Parking Bays 43

Appendix A

GLOSSARY OF TERMS 44

Appendix B

DESIGN EXAMPLE 46

REFERENCES 48

BIBLIOGRAPHY 49

Further Reading 49

Contents


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THIS GUIDE supersedes the first edition (with the

title 'Pavement Design for Residential Streets')

published by the Association in 1997. In addition to

routine updating of the content, the new guide covers

a wider range of elements for which concrete can be

used in residential subdivisions. The most significantchanges distinguishing it from the first edition are:

Revision of the recommended pavement

thicknesses to reflect the latest changes adopted

by Austroads in their 'Guide to the Structural

Design of Road Pavements' published in 2004.

Expansion of the text covering all design and

construction aspects of concrete pavements.

The inclusion of material on subsidiary elements

typically required in land development, ie

footpaths, bikeways, thresholds, parking baysand kerb-channels.

For many years, residential streets were designed

primarily for vehicular access. Today, however, equal

consideration is given to residents, cyclists and

pedestrians. Traffic calming techniques are used to

provide a safe environment for all. In addition, the

road reserve is now being used as a landscapeelement to enhance the environment and at the same

time add value to the adjoining properties. Concrete

pavements have become a key element in enhancing

the streetscape as concrete easily provides a variety

of colour, textures and forms. The durability of

concrete provides the pavement with a long service

life requiring minimal maintenance.

This guide covers the design, detailing and

construction of concrete pavements for residential

streets, bikeways and footpaths. It has been prepared

to assist designers and contractors with the designand, more importantly, the detailing of concrete

pavements to ensure that the pavement provides a

high level of service ability during its design life. The

content of the manual is arranged in the order in which

the design and construction processes are performed.

Residential streets can be classified as minor, local

access or collector and, as safety is important, are

designed for vehicle speeds of 60 km/h and less.

Pavement widths can vary from a single lane for

minor roads to four lanes or more for collector roads.

A kerb and channel or dish drain is generallyprovided along the edge of the pavement to facilitate

drainage. For narrow roads, a one-way crossfall can

be adopted to minimise stormwater drainage.

Alternatively, the pavement can have a central dish

drain that does not require any kerb and channel.

Traffic volumes have an Annual Average Daily Traffic

(AADT) in the range of less than 150 vehicles for minor

roads and up to 2000 vehicles for collector roads.

4

01 IntroductionPreface


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2.1 DEFINITIONS

The elements of a typical concrete pavement are

shown in Figure 2.1. For this guide the key terms are

defined as follows:

Base The main structural element of the concretepavement.

Reinforcement Reinforcing bars or reinforcing fabric

complying with AS/NZS 4671 Steel Reinforcing

Materials1.

Subbase The layer of selected material placed on

the subgrade.

Subgrade The natural or prepared formation on

which the pavement is constructed.

Wearing surface The trafficked surface and the top

surface of the base.

Additional terms used in this manual and common for

residential streets are defined in Appendix A.

Figure 2.1 Elements of a concrete pavement

2.2 PAVEMENT TYPES

The two pavement types covered in this manual are

illustrated in Figure 2.2.

Plain Concrete Pavement (PCP) This pavement type

contains no drying shrinkage reinforcement except in

irregular-shaped slabs or slabs containing pits.

Transverse contraction joints are placed across the

pavement at approximately 3- to 4-metre intervals.

Plain concrete pavement is the lowest initial cost

concrete pavement, with the simplest construction

method. Where ground conditions are prone to large

uneven settlements it should be used with care due

its lack of a positive connection across contraction

joints and risk of unplanned cracking mid-slab.

Reinforced Concrete Pavement (RCP) This type of

pavement is characterised by transverse contraction

joints typically spaced in the range 10 to 15 metres.

Steel reinforcement is provided to control, but not

prevent, cracking which may occur between these

joints.

Reinforced Concrete Pavements may be used on

most subgrades, including those prone to uneven

settlements.

For a particular application, both of these pavement

types would have the same thickness, the

reinforcement is used to control drying shrinkage

cracking and is not designed to add to the load-

carrying capacity of the pavement.

Figure 2.2Concrete pavement types

5

02 Terminology

SUBGRADE

SUBBASE(desirable)

CONCRETEBASE

Wearing surface Steel reinforcement (as required)

JOINTED UNREINFORCED (PLAIN) CONCRETE PAVEMENT

3 to 4 m

JOINTED REINFORCED CONCRETE PAVEMENT

10 to 15 m


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The choice between these two pavement types

requires an assessment of a number of factors. In

general, a jointed unreinforced pavement offers a

lower construction cost and a simpler construction

procedure for straight paving runs. A jointed

reinforced pavement will cost slightly more to

construct, but offers considerable simplification in

designing joint layouts for intersections and in turning

areas of cul-de-sacs or minor roads. It will also often

require less future maintenance. On problem sites, the

use of a reinforced pavement may be prudent to

control unplanned cracking.

In many projects there will be a case for a mixture of

both pavement types to utilise the benefits of each.

Continuously Reinforced Concrete Road Pavement

(CRCP) This pavement type is rarely used for

residential streets due to its higher cost; it is used

mainly on major road projects. Transverse contraction

joints are not formed in the pavement since the

continuous longitudinal reinforcement is designed to

limit the width of any cracks that form. CRCP

pavements develop transverse cracks at spacings in

the range of 0.5 to 2.0 metres. The design procedure

for this type of pavement is covered in the Austroads

pavement design guide2.

Steel Fibre Reinforced Concrete Pavements are

commonly used at roundabouts, intersections and

bus bays where there is an unavoidably high

incidence of odd-shaped slabs. Steel fibre concrete is

easy to place in odd shapes and provides good

control of shrinkage stresses in acute slab corners

where conventional reinforcement is of little benefit.

A wide range of steel fibre size and type is currently

available and the fibre dosage required to achieve a

given performance varies considerably. Design

procedures therefore need to recognise thecharacteristics of the fibre to be used and guidance

should be sought from the fibre supplier.

3.1 STREETSCAPE DESIGN

Residential streets have traditionally been designed by

engineers and surveyors solely to meet the needs of

vehicles. Today the emphasis has changed to creating

a streetscape meeting the broader needs of people,

rather than just providing for the carriage of vehicles.

If the designer starts from the viewpoint of streets as

being an important open space for the community,

then a much more pleasing environment results.

These sentiments are not new. Edna Walling, the

famous Australian landscape designer (quoted by

Matthews3), expressed the sentiment that 'streets are

the front gardens of our nation'. The street that

embraces this concept creates a much more livable

environment than the street designed on the vehicle-

only basis. In this scenario, residents, pedestrians,

cyclists and motorists all have equal status.

AMCORD4 provides guidelines for the overall

planning, street design and construction to also cater

for pedestrians, cyclists and public utilities. AMCORD

encourages both the development of attractive

streetscapes in new residential areas and provides

guidance on existing streetscapes in established

areas. The resultant narrow pavement widths and

various traffic-calming techniques combined with the

need to consider aesthetics mean that a versatile

pavement material is required.

Concrete can provide a variety of colours, textures and

forms to achieve different appearances. Concrete can

easily be constructed to the narrow trafficable widths

often required for traffic calming because it does not

need specialised laying equipment and rollers.

To provide pleasant streetscapes, an overall landscape

plan is developed for the full road reserve. Apart from

the pavement, other design elements include:

street furniture;

walls and fences; and

vegetation and landscaping.

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03 Streetscape


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7

This enables the street, or area, to have a distinctive

theme or feel.

The plan developed must be appropriate for the areaand must consider various values including

historical;

cultural and social; and

environmental.

The fundamental objective in street design is to make

streets safe for pedestrians, cyclists and motorists.

Measures to limit vehicle speed, provide adequate

turning facilities, parking bays for visitors, site access

and to maximise visibility are essential requirements.

3.2 DECORATIVE SURFACE FINISHES

3.2.1 General

Concrete pavements offer a significant advantage

over other forms of paving in that they can be

provided with a very durable, skid-resistant surface in

both dry and wet condition which can have a wide

variety of appearances. For example, a coarser

texture to improve skid resistance can be provided at

curves, intersections and on steep gradients, while

the wide variety of colours and forms achievable in

the surface enable the pavement to form an integral

part of the streetscape. The texturing and colouring is

done as part of the concreting process5.

Tyre/road noise from the wearing surface of residential

streets is not a relevant issue since at low traffic

speeds (ie < 60 km/h) noise from the vehicle's power

train is the dominant noise source. Tyre/road noise is

dominant only at speeds of about 80 km/h or more.

Therefore, with residential streets it is important to

focus on safety. Providing a rough texture to the

wearing surface is one method of maintaining low

vehicle speeds.

Decorative concrete has been used in many new

residential developments to:

provide prestige to selected pavement areas

(eg signature statement);

provide a unique themed look for individual

projects;

increase delineation for different pavement

functions, such as through pavements, pedestrian

crossings and parking areas;

highlight the entrance to smaller streets from the

main thoroughfare;

reduce vehicle speeds in residential areas.It is important with all finishes that effective quality

control methods are put into place to ensure

durability. In all applications the concrete should be

well compacted and properly cured. For more

information see Guide to Concrete Construction6.

3.2.2 Simple Finishes

Simple surface textures can be applied using steel

tynes, brooms, wood floats or a dampened hessian

drag.

A suitable low-speed surface to provide adequate

skid resistance can be produced by either wood

floating or by dragging hessian over the surface of

the finished concrete. Brooming or tyning can be

used where greater skid resistance is required.

A tyned texture is usually specified to provide

adequate skid resistance on high-speed roads where

vehicle speeds are equal to or in excess of 70 km/h

and aquaplaning is also a concern. It is not normally

used or required on low-speed residential streets.

Alternatively, a tyned texture may be used on steep

grades (ie >16%) to improve traction for vehicles.

See Road Note 247

3.2.3 Stamped Concrete

Stamped concrete can be used to imitate cobbles,

brick, timber and slate. Almost any texture can be

achieved including timber board textures. Care must

be taken to avoid a surface that is too smooth. A

secondary process may be required to provide

adequate skid resistance.

Depending on the texture and depth of the pattern

selected, various levels of ride quality can be

achieved. This variation can be used to advantage in

residential areas to encourage a low-speed

environment and to alert drivers to intersections,

pedestrian slow points, parking areas and bus stops.

Stamped concrete patterns are formed by using

integral (full-depth) coloured concrete or by

broadcasting and trowelling a coloured dry shake into

the surface of the fresh concrete in two applications.

A minimum concrete strength of 32 MPa is

recommended. Depending on the texture required for

the finished wearing surface, flexible moulds or


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stamping tools (metal grids) are placed and worked

into the surface of the concrete. The application of

uniform force to the rubber moulds or stamping tools is

required to ensure a uniform impression is achieved.

Prior to stamping with the flexible moulds, a release

agent is first broadcast onto the surface to aid in

release. Alternatively, the pavement is covered with a

sheet of plastic prior to the application of the stamping

tools in order to give rounded edges to the indentations.

Residue release agents/powders should be removed

by stiff brushing, detergent washing or high-pressure

hosing. These processes should be undertaken

following 3 days of curing. To remove any additional

residue, an application of a mild acid wash, at a ratio

of 1 part acid to 25 parts water is suggested. This will

remove remaining release agents/powders and

slightly etch the surface, providing a key for

subsequent sealer coats. The surface should be

rinsed with clean water to neutralise the acid. A sealer

may then be applied to the completed pavement to

protect the wearing surface and enhance the colour

as required. Stamping does not replace the proper

procedure of jointing within the pavement, as the

depths of indentations are too shallow to act as

weakened-plane joints.

For more information on stamping, see Briefing 018.

3.2.4 Stencilled Concrete

Stencilling can be used to achieve a variety of brick

and tile-like finishes, complete with mortar lines.

Patterns available include running bond, stacked

bond, basket weave, herringbone, square tile,

cobblestone and cobble fan. Additional special

stencils are available, including circular patterns,

motifs and street names.

Installing a contrasting bond pattern to pavementedges and joints often enhances the appearance of

stencilled areas to highlight joints, penetrations and

changes in gradient.

Placing a cardboard stencil into the surface of the wet

concrete forms a stencilled surface. A minimum

concrete strength of of 32 MPa recommended. A

coloured dry shake surface hardener consisting of

oxides, cement, fine aggregate and hardeners is

spread onto the surface by hand-casting and

trowelling, in two applications, to achieve a uniform

colour and thickness. When the surface hashardened, the cardboard stencil is lifted from the

pavement. A sealer may then be applied to the

completed pavement to protect the wearing surface

and enhance the colour as required.

Effective quality control is very important when

stencilling concrete. The processes for stencilling are

relatively simple. The timing of each stage and the

application of dry shakes are, however, critical to the

success and durability of the finish.

For more information on stencilling, see Briefing 018.

3.2.5 Exposed Aggregate

For an exposed aggregate finish, one to three

millimetres of surface paste is removed to expose the

coarse aggregate to achieve an attractive finish which

may improve skid resistance. By varying the colour of

the aggregate and cement paste, in conjunction with

the depth of exposure, a variety of visual effects can

be achieved. Concrete mixes with gap-graded

aggregates give the best visual stone density onexposed aggregate surfaces. Alternatively, special

8

RUNNING BOND BASKET WEAVE

HERRINGBONE STACKED BOND

150-mm SQUARE TILE 200-mm SQUARE TILE

COBBLE STONE COBBLE FAN

Figure 3.1 Stencil patterns many of the patterns

offered by segmental paving are replicated by stenciland stamp techniques


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coloured aggregates may also be 'hand seeded' onto

the surface. A minimum concrete strength of 32 MPa

is recommended.

An exposed aggregate finish is obtained by applying

a set-retardant to the surface of the concrete

approximately 2 to 3 hours after placing and then

covering the pavement with plastic sheeting. After

18 to 24 hours,1 to 3 millimetres of the cement paste

is removed using a low-pressure hose and a stiff

broom or by dry mechanical brushing, to expose the

aggregate. The finish can be achieved without a

surface retardant, but timing is very critical and

working times will be much shorter.

For more information on stencilling refer to Briefing 029and Road Note 6410.

3.2.6 Coloured Concrete

Coloured concrete may be used for any form of

concrete pavement. The concrete is normally

coloured with the use of metallic or synthetic oxides,

either mixed through the concrete (integral colouring)

or worked into the surface as a 'dry shake'. Integral

colouring ensures that the colour has the same life as

the concrete, whereas with the dry-shake method the

colour may be lost with surface wear. Contrastingcolours are often used. For example, one colour for

'through pavement' areas and another colour for

traffic islands, medians, parking or pedestrian areas.

3.3 TRAFFIC CALMING

Traffic calming is achieved by the use of a variety of

techniques to encourage driving at lower speeds,

thus improving pedestrian safety and the amenity of

the area. Vehicles can be restricted to the selected

design speed through:

limiting the length of straight sections in the

street;

introducing bends;

controlling on-street parking;

incorporating speed-control devices.

Limiting the length of the straight path in which a

vehicle can be driven is possibly the most important

traffic safety measure since it limits the speed that a

vehicle can physically attain. The low-speed

environment provides more reaction time for drivers

and pedestrians, and if there is a collision it reducesthe severity of the accident. Straights can be limited

by winding the street through the road reserve either

by general curves or by off-set straights. Interrupting

long straights with speed-control devices is another

alternative.

Speed control devices include:

roundabouts;

skewed intersections;

slow points;

narrow pavements;

curved or staggered alignments (limiting the

length of straights);

threshold treatments;

change of surfacing;

speed humps.

Landscaping can also be used to modify driver

habits, but it must be planned not to impair vision.

Concrete can be used in all of the above techniques

and with imagination and appropriate landscape

design can achieve an attractive streetscape. A

lateral change in direction is usually less obtrusive to

drivers than a speed hump, see Figures 3.2 and 3.3.

9

Planting area

Figure 3.2Slow point

Planting area Road entr y thresholdParking bays

Figure 3.3Staggered alignment


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10

4.1 GENERAL

This section outlines the various elements considered

in determining the design thickness of the concrete

base and detailing of the pavement in order that it will

remain functional throughout its design life. Each

element is then discussed separately in Sections 5

through to 10.

4.2 SITE INVESTIGATION

The site investigation consists of undertaking a soil

investigation, estimating the design traffic and

carrying out a site survey.

The soil investigation determines the characteristics

and strength of the natural soil on which the pavement

is to be constructed. The soil properties influence

subgrade preparation, the need for a subbase and

the determination of the concrete base thickness.

The thickness design procedure for concrete

pavements incorporates not only the number of axle

loads and commercial vehicle axle groups (CVAG) but

also the spectrum of the axle loadings. Axle loads are

not converted into equivalent standard axles (ESAs)

as in designing flexible pavements. Thicknesses for

lightly trafficked residential streets are controlled by

construction, service or delivery vehicles since axle

loads from cars have little impact on base stresses.

For collector and other street types, bus traffic or

other heavy commercial vehicles will usually control

the thickness.

It is necessary to carry out a site survey for the

proposed pavement to evaluate the site topography

and features such as existing or proposed public

utilities which may influence the pavement design.

Drainage of residential street concrete base and

subbase layers is not considered as crucial as for

flexible pavements. This is because, unlike flexible

pavements, the concrete base provides the vast

proportion of the load-carrying capacity of the

pavement. Also, unlike granular pavement layers, the

strength of the hardened concrete pavement is not

reduced by water.

4.3 THE SUBGRADE

The high modulus of elasticity of concrete enables

concrete pavements to distribute loads over large

areas. Concrete pavement thickness is therefore not

particularly sensitive to the strength of the subgrade.

It is much more important that the subgrade provides

reasonably uniform support.

Subgrade uniformity is influenced by moisture/density

control, variations in material type and expansive

soils. These are discussed in detail in Section 6.3

Subgrade Uniformity.

Where highly expansive subgrades occur, a cover of

low-volume-change soil over the full width of the

subgrade is recommended. This is also recommended

where moderately to highly expansive subgrades

occur in temperate areas subject to prolonged

periods of dry weather Alternatively, a layer of the

existing soil may be stabilised by the addition of lime

and/or cement. This is discussed in detail in

Section 6.4 Stabilised Subgrades.

4.4 THE SUBBASE

As previously stated, the concrete base provides the

pavements major structural capacity. The functions of

a subbase in a concrete pavement include:

providing uniform support to the concrete base;

reducing deflection at joints and hence

maintenance of effective load transfer across

joints (see RTAs roundabouts publication11).

assisting in controlling volume changes in

moderately to highly expansive soils;

eliminating erosion and pumping of the subgrade

(especially at joints) as a potential failure mode

(generally for heavy trafficked pavements);

providing a stable working platform for pavement

base construction.

For heavily trafficked roads (beyond the scope of this

guide) cement stabilised or lean-mix concrete

subbases may be used to control subbase erosion due

to pumping (in accordance with the Austroads guide2).

04 Design Process


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4.5 CONCRETE

The principle properties of a pavement material

requiring consideration are surface finish, flexuralstrength, skid resistance and durability. The various

types of surface finishes are discussed in Section 3

Streetscape, while the other properties are discussed

in detail in Section 8 Concrete.

4.6 JOINTS

4.6.1 General

Joints are provided in a concrete pavement for

construction considerations, to minimise the risk of

unplanned cracking and to avoid conflict with otherstructures and/or penetrations. The types of joints that

may be required in concrete pavements covered by

the guide are:

Contraction joints control transverse and

longitudinal cracking in the pavement due to

drying shrinkage and warping. Reinforcement

placed in the upper third of the pavement (except

for thin pavements) is frequently used in

conjunction with contraction joints to achieve this

objective.

Construction joints divide the pavement intosuitable lengths and widths for construction

purposes.

Isolation joints isolate pavement elements from

each other or other structures in certain

situations.

Expansion joints accommodate expansion of

the pavement, primarily due to elevated

temperatures.

These are discussed in detail in Sections 10.2

Contraction Joints, 10.3 Construction Joints,

10.4 Isolation Jointsand 10.5 Expansion Joints.

4.6.2 Joint Sealants

It is recommended that pavement joints designed to

accommodate movement should be properly sealed.

This is discussed in detail in Section 10.6 Joint Sealing.

4.6.3 Joint Layout

After determination of joint types and slab dimensions,

a joint layout can be prepared. The principal aim

should be to develop a simple layout to maximise the

use of uniform slab dimensions. This is discussed indetail in Section 10.7 Joint Layout.

5.1 GENERAL

The site investigation covers three areas: soil

investigation, traffic estimation and site survey. The

time devoted to these preliminaries will vary

according to the size and status of individual project

and previous experience. However, to meet the

design objectives, each of the areas warrants some

consideration.

5.2 SOIL INVESTIGATION

An investigation should be made of the

characteristics and strength of the soil on which the

pavement is to be constructed.

The soil properties will influence subgrade

preparation; the need for, and specification of, a

subbase; and the thickness of the concrete base.

However, it should be noted that the design thickness

of the concrete base is not particularly sensitive to the

subgrade strength.

For very weak subgrades having a CBR of less than

2% (refer to Section 6.2 Subgrade Support), the

subgrade will require improvement, either some form

of stabilisation (ie lime/cement) or additional filling in

order to support construction loads. Austroads

pavement design guide2 provides more information.

5.3 TRAFFIC ESTIMATION

The performance of a residential street pavement is

affected by the nature and level of traffic loading

encountered over its design life. Pavement

thicknesses for lightly trafficked residential streets are

generally controlled by service or delivery vehicles.

Flexible and rigid pavement designs are both based

on axle loads. However, rigid pavement design uses

commercial vehicle axle groups (CVAG), which may

include the spectrum of axle loads, in contrast to

converting axle loads to equivalent standard axles(ESA) for flexible pavements.

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05 Site Investigation


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CVAG spectrum data are not readily available for

residential streets. However, during the development

of ARRB Special Report No. 4112, load spectrum data

were collected for 57 local road sections, sufficient to

give a reasonable estimate of the average and

90 percentile values for each traffic category listed in

Table 5.1.

The 90 percentile values can be taken as

conservative estimates of design traffic, taking into

account construction traffic during the staging of

subdivisional work.

The designer may undertake a traffic survey or use

existing data to determine the design number of

CVAG. If no traffic data is available, the values shownin Table 5.2 may be used.

The design life of concrete pavements is normally

40 years compared with 20 to 25 years for flexible

pavements. It is important when comparing pavement

alternatives in a life-cycle-costing analysis that the

same analysis period is used for all pavement types.

With a concrete pavement, the additional thickness

required for the difference between a design life of

40 years and 20 years is not significant compared to

the total thickness of the pavement.

TABLE 5.1 Street Classifications (APRG 199813

Table 13.7.2)

AADT limits Percent AADCV

Street Type (two-way) CVs (two-way)

Minor: 3090 3 13*

Local access:

without buses 400 4 16with buses 500 6 30

industrial 400 8 32

Collector roads:

without buses 1200 6 72

with buses 2000 7 140

Annual Average Daily Traffic Annual Average Daily Commercial Vehicles (over 3 t gross mass) Commercial vehicles

* These traffic volumes usually are not halved for one-way traffic due

to narrowness of Minor Roads

5.4 SITE SURVEY

5.4.1 General

It will be necessary to carry out a site survey for the

proposed pavement. The site topography, drainage

and surface features such as existing or proposed

public utilities will influence the pavements geometric

design.

5.4.2 Public Utilities and Service Reinstatement

In both construction and reconstruction projects, the

planning lead time should allow for installation or

relocation of public utilities. The various mains and

services can be installed in advance of pavement

construction or, in the case of electrical services,

conduits can be placed with draw wires for later

insertion to the requirements of the relevant authority.

The use of conduits for various services also allows

easy later modifications or maintenance. It is worth

remembering that additional conduits placed in

advance of pavement construction will cost less and

cause much less inconvenience than future road

openings or boring.

An advantage of concrete pavement is that the

location of utility conduits can be marked in the

pavement surface.

It is important to design a concrete pavement with

services in mind. Other options to allow for later

reinstatement, where aesthetics and colour matching

are of concern include:

contrasting coloured or textured strips of concrete;

removable pavement types, such as pavers or

pitchers across the pavement.

5.4.3 Drainage

Residential streets are not heavily trafficked by highaxle loadings. Inadequate drainage is more likely to

affect the performance of granular materials in the

subgrade and subbase rather than that of the

concrete base. With concrete pavements, the

concrete base provides the vast majority of the

structural strength. With residential street concrete

pavements, little benefit for high cost is therefore

achieved by the provision of subsurface drainage.

Other considerations such as presence of spring

activity or other known excessive moisture exposure

may therefore govern the need for subsurface drains

for residential streets.

12


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Longitudinal and cross gradients for concrete

pavements are the same as for other pavements. The

choice of one-way (for narrow pavements) or two-way

crossfalls will influence both the location of construction

joints and the direction of paving runs. The narrow

pavement widths resulting from AMCORDs

recommendations allow a one-way crossfall to be

adopted with resultant cost savings. Surface drainageis minimised and this results in only one storm water

drainage line being needed for these pavements as

shown in Figures 5.1 and 5.2.

Integral kerb and channel, kerb only, roll or mountable

kerbs, and dish drains can be readily provided.

Kerb-inlet type gullies are preferable for concrete

pavements, as they do not intrude into the carriageway.

However, grated gully pits can be accommodated in

a concrete pavement, detailed procedures are

provided in Section 10.7 Joint Layout.

13

TABLE 5.2 Design commercial vehicle axle groups by street type (based on APRG 199813 Table 13.7.4)

Design life Annual traffic Mean axle Design CV axle

Street Type (years) growth rate (%) Lane factor groups per CV groups

Minor:

single-lane traffic 20 0 2 2.0 1.5 x 104

40 0 2 2.0 2.5 x 104

two-lane traffic 20 0 1 2.0 2 x 104

40 0 1 2.0 4 x 104

Local access:

without buses 20 1 1 2.1 1.5 x 105

40 1 1 2.1 3 x 105

with buses 20 1 1 2.1 2.5 x 105

40 1 1 2.1 5.5 x 105

industrial 20 1 1 2.3 3 x 105

40 1 1 2.3 6.5 x 105

Collector roads:

without buses 20 1.5 0.9 2.2 6.5 x 105

40 1.5 0.9 2.2 1.5 x 106

with buses 20 1.5 0.9 2.2 1.5 x 106

40 1.5 0.9 2.2 3 x 106

One-way traffic volume to design lane volume For streets5 m width or where two-way traffic traverses a common wheelpath

Integral kerb

Sub-surface drain

Fall

Figure 5.1 One-way crossfall

Sub-surface drain

FallFall

Figure 5.2Central dish drain


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6.1 GENERAL

A reasonably uniform foundation is essential to the

good long-term performance of a concrete pavement.

An assumption that a concrete pavement will bridge

over a poor subgrade could lead to a false sense of

security. However, concrete pavements have been

constructed successfully on a wide range of poor

sites including floodplains, mine subsidence areas

and very weak soils.

6.2 SUBGRADE SUPPORT

6.2.1 General

The high modulus of elasticity of concrete enables

concrete pavements to distribute loads over large

areas. As a result, deflections are small and

pressures on the subgrade are low. Concrete

pavement thickness is therefore not particularly

sensitive to the strength of the subgrade. As stated

above, it is much more important that subgrade

support be reasonably uniform with no abrupt

changes in the degree of support.

Subgrade strengths for pavements have traditionally

been defined by determining the California Bearing

Ratio (CBR) of the founding material. A typical range

for weak to strong soils would be 2% to 15%. This

guide uses the following very broad categories for

which pavement designs have been prepared:

In selecting the soil strength category (or a 'Design

CBR'), the designer is attempting to assign a value

that best represents close to the weakest soil strength

condition to be endured during the design life. This

may or may not be present at or during construction,

and should be a conservative rather than optimistic

value, for several reasons:

It is difficult to accurately predict changes in soil

strength for 20 or more years into the future. The

effectiveness of pavement drainage and the large

range of environment influences often introduce

significant uncertainties;

The amount of test data on soil strengths is likely

to be limited; The designer usually has little direct control of

construction variables or the future maintenance

effort;

Additional construction costs of an adequate

pavement are invariably relatively minor in

comparison to the cost of the remedial works

associated with a deficient design.

6.2.2 Poor Strength Soil Foundation

Poor strength soils are those that would normally

require pre-treatment if the pavement were to beconstructed while they are in that state. This

pre-treatment may comprise:

placing of a stronger fill material to provide a

better construction platform;

chemical stabilisation using lime and/or cement if

soil conditions are accommodating; or

use of a geosynthetic as a separation layer.

The requirement for subgrade improvement may not

arise if the poor soil strength is not evident during

construction, such as may occur with heavy clays

during summer. For this reason, there are often cost

savings or expediencies to be gained if the

construction timing is negotiable.

Pavement designs given in Section 9 Thickness

Designare inclusive of 'Poor soil strength' based on a

design CBR of 2%.

Some situations where these soil conditions may exist

are:

along river valleys and flood plains where alluvial

soils may predominate;

14

06 Subgrades

TABLE 6.1 CBR values used for pavement

designs in this manual

Strength of soil foundation Design CBR (%)

Poor 2

Moderate` 5

High 10

Very high 15


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in zones subject to poor drainage and inundation;

or

where climatic conditions result in high moisturecontent.

6.2.3 Moderate Strength Soil Foundation

These soil conditions generally would not require

special pre-treatment of the soil apart from compaction

prior to the placement of the pavement. However, in

except for loose frictional soils or granular materials,

most subgrades will benefit from minimal disturbance,

as the insitu undisturbed soil structure will have an

intrinsic strength that is worth preserving. Many road

authorities generally avoid routine reworking of insitu

subgrades in favour of soft spot identification by

proof-rolling, followed by local improvement.

Pavement designs given in Section 9 are inclusive of

'moderate soil strength' based on a design CBR of 5%.


are:

zones which have good drainage,

eg embankments;

climatic conditions causing perennially low soil

moisture content; or

sands and low plasticity clays not subject to

saturation.

Generally, Poor Strength soils and Moderate Strength

soils are the dominant soil strengths.

6.2.4 High Strength Soil Foundation

High strength soils have been assigned a design CBR

of 10%, which equates to the maximum design strength

that State road authorities generally allow. Designs in

Section 9 are also inclusive of this soil strength.

A design CBR of 10% should be assigned onlyfollowing expert advice and inspection, and preferably

a detailed site investigation.


are where:

native soil comprises weathered rock;

good quality selected fill has been placed with

good compaction;

soil has or will be stabilised and laboratory testing

has confirmed high strengths; or

pavement is constructed in a semi-arid andwell-drained locality.

It is expected that high strength soils would only

rarely occur within significant lengths of a proposed

pavement. Some exceptions might include a sandy

coastal environment or through hilly areas of rock or

gravel deposits.

6.2.5 Very High Strength Soil Foundation

Very high strength soils have been assigned a design

CBR of 15%, which is the maximum design strength

that most State road authorities permit. Designs in

Section 9 are inclusive of this soil strength.

As with the assignment of a CBR for a high strength

soil, the CBR for very high strength soil should also

be assigned only following expert advice andinspection, and a detailed site investigation.


are where :

native soil comprises rock and is levelled using a

granular layer including, where appropriate, a

granular drainage layer;

structural fill (a designed layer of laboratory-tested

material) has been placed using controlled

compaction;

select or structural fill has or will be stabilised and

laboratory testing has confirmed very high

strengths; or

a granular subbase 100 mm thick is placed on a

subgrade characterised as a high strength soil.

Unless such soil conditions already exist, the benefits

gained by using this soil strength are often marginal

compared to the cost of providing such a foundation.

6.3 SUBGRADE UNIFORMITY

6.3.1 General

Factors that influence subgrade uniformity are:

moisture/density control;

variations in material type;

expansive soils.

6.3.2 Moisture/Density Control

In clay or other fine-grained soils, subgrade uniformity

can be enhanced by proper moisture/density control

during construction. Two conditions can lead to

movement within these soils in service:

Soils that are compacted too dry, or are allowed

15


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to dry out before paving, resulting in subsequent

moisture gain.

Subgrades with varying insitu moisture contents,resulting in differential moisture change.

After some time in service, clay-type subgrades may

reach an equilibrium moisture content approaching

the plastic limit, typically slightly below the laboratory

optimum moisture content. Once this condition is

reached, further moisture change and the tendency to

swell/shrink will be reduced.

As a general practice, it is recommended that clay-

type subgrades be compacted at moisture contents

slightly below the optimum values determined in the

laboratory.

For low-plasticity or non-cohesive subgrades, the

same moisture/density controls used for other

pavements apply to concrete pavements.

6.3.3 Variations in Material Type

Any abrupt changes of material type should be

eliminated during subgrade preparation. Selective

grading or mixing of material to provide a transition

between material types can control this factor.

6.3.4 Expansive Soils

Where moderately to highly expansive subgrades

occur, a cover-layer of low-volume-change soil over

the full width of the subgrade is recommended.

Alternatively, a layer of the existing soil may be

stabilised as discussed in Section 6.4 Stabilised

Subgrades.

The function of the cover-layer is to minimise changes

in moisture content and hence volume changes in the

underlying expansive soil. The appropriate thickness

for non-expansive cover layers will depend on

expected site conditions before and after construction

(depth of fill, etc) and on local experience.

6.4 STABILISED SUBGRADES

In many lightly trafficked streets or parking areas,

subgrade stabilisation can provide a suitable subbase

for both the pavement and construction equipment.

Not all pavements will require subgrade stabilisation.

Very weak subgrades (CBR values of 2% or less) will

probably require some form of stabilisation in order to

support construction loads.

The stabilisation of clay subgrades will enhance their

stability under conditions of alternate wetting and

drying and will extend the construction period by

providing an all-weather working platform.

6.5 SUBGRADE PREPARATION

In addition to proper moisture/density control, the

design drawings and specification should cover two

points that will assist in achieving subgrade uniformity:

The subgrade should be prepared for the full

pavement formation, extending at least to the

back of kerbs.

The reinstatement of utility trenches during

construction should be closely supervised to

ensure that the requirements of the subgrade

uniformity are achieved. The use of controlled

low-strength materials flowable fills that do not

require compaction and do not settle after

construction should be considered (see

Matthews14).

16


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7.1 GENERAL

The function of the subbase layer in a concrete

pavement should be distinguished from the equivalent

layer in a flexible pavement. As the concrete slab

provides the pavements major structural capacity, it

will usually be uneconomical to provide a subbase

merely in order to reduce the concrete thickness.

The functions of a subbase in a concrete pavement

are related to future serviceability and are listed in

Section 4.4 The Subbase.

The Portland Cement Association15 notes that

concrete pavements designed to carry less than

100 to 200 heavily loaded vehicles per day do not

suffer from erosion damage, and so do not require a

subbase for this reason alone. However, the other

functions of a subbase may be required on a specificproject. Given that erosion is not a major concern for

concrete pavements under light traffic, such as

residential streets, the importance of sub-surface

drainage is reduced. For industrial estates where

heavy vehicular traffic is expected, a subbase will be

required.

7.2 SUBBASE THICKNESS AND

WIDTH

As the subbase does not contribute significantly to

the load capacity of a concrete pavement, its

thickness is empirically determined. Minimum

suggested subbase thicknesses are shown in

Table 7.1. Where kerbs are provided, the subbase,

irrespective of type, should extend at its full depth to

at least the back of kerbs or other edge stops. It

should be placed at this width in advance of kerbs to

provide for their support. On streets that have no

integral kerbs, it is recommended that cement-treated

and granular unbound subbases extend at least

300 mm beyond each side of the carriageway.

7.3 UNBOUND SUBBASES

Granular subbase material may be composed of

sand-gravels, crushed rock, crushed slag, crushed

recycled concrete or a mixture of these materials. The

material should meet the following basic requirements:

Maximum size Not more than 1/3

of the subbase layer

thickness

Amount passing 75-m sieve 15% maximum

Plasticity index 6 maximum

Liquid limit 25% maximum.

Materials not complying with these requirements maybe used if they are suitably stabilised.

The material should be graded to permit compaction

that will minimise post-construction densification.

Recommended compaction requirements are the

same as for other pavements.

Where unbound subbases are used, the increase in

effective subgrade strength is minor and should be

ignored for design purposes.

7.4 BOUND SUBBASES

Residential streets are generally not heavily trafficked

by commercial vehicles and therefore do not require a

bound subbase to resist erosion. Erosion is not a

limiting factor with the performance of these

pavements.

When bound subbases are used, a significant

increase in the effective subgrade strength is

achieved. For bound subbases a cemented, not just

modified, material is required. The probable range of

cement contents for a cement-bound material will be

46% by weight of the untreated granular subbasematerial. However, modified subbase materials may

17

07 Subbases TABLE 7.1 Recommended subbase thickness (mm)

Subbase thickness for soaked subgrade

CBR values

Concrete base

thickness (mm) 5% 510% >10%

Up to 125 100

125150 125 100 100

Above 150 150 125 125


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be used for lightly trafficked pavements. The probable

range of cement contents for cement-modified

material will be 24% by weight of the untreated

granular subbase material (see Recycling Pavements

by Cement Stabilisation16).

7.5 SUBBASE CONSTRUCTION

The subbase should be trimmed to crossfalls and

surface tolerances as would apply in other

pavements, to avoid undesirable fluctuations in the

concrete base thickness. Finished surface level

tolerances should be +0 mm to 10 mm to ensure the

full base layer thickness is cast.

For bound subbases, the longitudinal jointing, if it

occurs (not usual), should be arranged so the

longitudinal joints in the subbase do not occur within

200 to 400 mm of longitudinal joints in the concrete

base layer.

8.1 GENERAL

The principal properties required by the concrete

base are

flexural strength;

skid resistance; and

durability.

The designer is mainly interested in the properties of

the hardened concrete. However, since concrete is in

a plastic condition when placed; its placing,

compaction, finishing and curing are of utmost

importance in achieving the hardened concrete with

the desired properties.

8.2 STRENGTH

The strength of concrete used in pavements is usuallyspecified in one of two ways:

Compressive measured by crushing a cylinder

along its vertical axis (AS 1012 Parts 8 and 917)

Flexural measured by breaking a beam in

flexure (AS 1012 Parts 8 and 1117)

When, under vehicular traffic, a concrete pavement is

loaded to the point of fracture, the concrete fails in

flexure rather than compression. For this reason, the

concrete thickness design is based on flexural

strength rather than compressive strength. Flexural

strength grades in the range of F3.5 MPa to F4.25 MPa

are typically specified for concrete pavements.

Compressive strength testing is usually used as an

indirect measure of flexural strength.

A 28-day 4.25-MPa average flexural strength will

typically be obtained by a 28-day characteristic

compressive strength in the range of 3240 MPa.

Where no information is available the designer may, for

the thicknesses given in this manual, conservatively

assume either 4.25-MPa flexural and specify 40-MPa

compressive; or 3.50-MPa flexural and specify32-MPa compressive strength concrete.

18

08 Concrete


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8.3 SKID RESISTANCE

8.3.1 Factors Affecting Skid Resistance

To reduce the risk of skidding, a suitable surface

texture must be provided. The skid resistance of a

surface is measured by various means, from truck-

mounted devices to hand-operated portable devices.

Skid resistance is the ability of a surface to provide

friction to a reference tyre or slider, usually measured

wet. The units of skid resistance are measures of

coefficient of friction (below unity) or an index

representing the percentage of friction (index is

below 100).

The surface texture is divided into a micro-texture and

a macro-texture. At low speeds skid resistance is

primarily provided by the micro-texture. By definition,

a micro-texture has a wavelength of less than 0.5 mm

and typically a smaller height or texture depth of less

than 0.2 mm. Therefore, micro-texture is the

'roughness' felt by rubbing ones thumb across

sandpaper, or in a pavement context, across the

concrete mortar (surface).

At speeds of travel in excess of 40 km/h in wet

weather, the next level of surface texture (macro-

texture) becomes increasingly important in providing

skid resistance, as tyres tend to aquaplane on a thin

film of water. Macro-texture, the texture one feels by

placing fingers in between stone chippings or over

hessian-dragged concrete or a tyned concrete

surface, provides channels for water to be squeezed

from the surface to permit rubber to micro-texture

contact, thereby providing some skid resistance.

For residential streets and bikeways where maximum

operational speeds are typically 60 km/h and less, the

micro-texture has the greater influence on skid

resistance.

8.3.2 Other Factors which Influence Skid

Resistance

Abrasion resistance of the surface slows the rate of

decrease of skid resistance with time and trafficking.

For heavily trafficked pavements with traffic of

3 tonnes or more18, a minimum 32-MPa concrete isspecified to enhance the abrasion resistance.

Sand and fine aggregate particles contribute the

major 'roughness' component of the mortar matrix; the

micro-texture. Sand with a high quartz (silica) content

is an exceptionally hard-wearing material; crushed

quartz sand generally has excellent durability and

angularity.

Coarser aggregate particles have a significant effect

on skid resistance only if they are exposed. If an

exposed-aggregate surface is constructed, a coarse

aggregate having a minimum Polished Stone Value

(PSV) is required. The typical minimum PSV value of

such aggregate is 48.

8.3.3 Skid Resistance Values

The most widely used skid resistance value is the

Sideways Force Coefficient (SFC) produced by the

Sideways Coefficient of friction Routine Investigation

Machine (SCRIM). Recommended investigatory levels

for road pavement surfaces are given in Table 8.1.

Note that investigatory levels are greater values than

threshold levels.

19

TABLE 8.1 Recommended investigatory levels for skid resistance

Minimum Grip No.*

Investigatory SFC levels (Max. vehicle speed km/h)

Road situation (VicRoads/RTA 1995) (Transport SA 2001)

Difficult sites steep grades, tight bends,

traffic signal approaches, roundabouts 55 0.500.55 (6080)

Urban arterial roads (undivided) 0.45 0.45 (60)

Rural arterial roads (undivided) 0.45 0.45 (110)

Urban lightly trafficked roads and bikeways 0.40 0.40 (60)

* The approximate conversion from Grip No. to the British Pendulum No. SRV (Skid Resistance Value) is: SRV = 100 x Grip No.


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20

Another measure of skid resistance is shown in the

right column, that given by the GripTester which

produces a value not exactly the same as, but very

similar to SCRIMs SFC value. If a portable British

Pendulum test device (a hand-operated device), is

used an approximate relationship of these values to

the Grip No. is provided in the footnote to Table 8.1.

8.3.4 Typical Skid Resistance Values for

Decorative Concrete Surfaces

Work carried out by the Cement & Concrete

Association of Australia19 on decorative finishes,

based on meeting minimum skid resistance values,

suggests the following generically described finishes

are suitable for residential streets.

Finish Comments

Rough cobblestone May present problems for

wheelchair users at road

crossings and for cyclists

in general

Coarse stencilled* Depends on durability (abrasion

resistance) of the finish

Broom Transversely applied

Wood float To produce fine macro-texture

Exposed aggregate A crushed aggregate must

be used

*Providing a homogenous and positive texture can be

imparted to the surface.

The above finishes are generically described. As the

actual skid resistance of a surface is dependent on

material types (sands, aggregates, etc) and how

these are used (finishing process, exposure of

aggregates, imparting of texture, etc) a wide range ofskid resistance values could result for any given

finish. Therefore it is not possible to provide a typical

skid resistance value for these finishes.

Hints for Improved Skid Resistance for Residential

Streets

Use silica or crushed silica sand.

Use crushed sand in preference to natural sand.

Use aggregates with a minimum percentage of

crushed faces where aggregate is likely to become

exposed during the pavements design life.

Where an exposed aggregate surface is to be

used, specify a minimum aggregate PSV of 48.

Avoid the use of a steel float; use a wood float ifno further texturing is to be imparted.

Avoid overworking of the surface as this tends to

bring more fines/slurry to the surface and may

reduce the surface durability.

Specify a minimum strength concrete; typically

32 MPa is specified for arterial pavements; the

absolute minimum value is 25 MPa.

Impart macro-texture to the surfacing; use wood

float, brooming, hessian drag, etc.

If a moulded stamped finish is used, additional

micro-texture may need to be implemented by

brooming or other surface application.

8.4 LUMINANCE

The procedure generally used for road lighting is to

make the road bright by beaming light against the

direction of the traffic. In this way, dark objects (nearly

all, particularly pedestrians, have a low reflection

factor) are contrasted against the brighter background

of the road surface. This compares with lighting by

vehicle headlights or by intense street lighting at forexample, pedestrian crossings, where the objects

themselves are illuminated.

Contrast, rather than discernment of detail is a key

visibility requirement as in ambient night-light

conditions, the human visual system loses sensitivity.

In providing the contrast, the pavement surface is

important in reflecting light to the eye of an observer;

both in wet and dry conditions. This luminance is

dependent on the surface texture and the colour, with

darker coloured surfaces absorbing more light than

lighter coloured surfaces. Researchers report that:

luminance levels of up to 30% greater can be

achieved by selection of a light coloured

surfacing20; and

to gain a similar brightness to that of concrete

roads, asphalt surfaces require a minimum of

15% of artificial brightener aggregates such as

quartzite or labrodorite21.

The top few millimetres of a concrete slab comprises

cement mortar mixed with fine aggregate particles;

usually sand-sized and less. Naturally occurring


22/50

sands often contain quartz, a very light coloured

mineral, which, with the light-coloured cement mortar,

provides a very light coloured surface. Aggregates,

which provide the bulk of the concrete mix, are,

unless specifically exposed, buried just beneath the

surface mortar and are not visible.

Other surfacings that have the aggregates exposed

or containing bitumen binder tend to present as dark

coloured unless, as mentioned previously, light

coloured aggregates are used.

Road surface texture is important in wet weather to

provide a diffusing effect on light rather than

producing a mirror-effectcalled specular reflection.

The spectrality of different surfaces is dependent onthe depth of texture and the degree of polish of

exposed aggregates. Durable surfaces, those which

retain their texture and resist polishing, will have

better long-term wet-weather luminance.

8.5 DURABILITY

Concrete should have adequate durability to resist

deterioration and wear under service conditions. To

achieve this, concrete should have sufficient abrasion

resistance and an adequate level of impermeability.

Measures taken to maximise the design strength of

the concrete will also enhance its durability. These

include:

good quality concrete;

proper placing and compaction;

proper curing (starting immediately after the

concrete has been finished).

The choice of a coarse aggregate does not greatly

influence the abrasion resistance of good quality

concrete. It is the fine aggregate (sand) which is at

the wearing surface.

The concrete pavement should comply with the

durability requirements of AS 360018; where limiting

values are generally strength requirements for

abrasion, ie pavements subject to:

Light pneumatic-tyred traffic

(vehicles up to 3 t gross mass) 25 MPa

Medium or heavy pneumatic-tyred traffic

(vehicles heavier than 3 t gross mass) 32 MPa

8.6 WORKABILITY

The workability of plastic concrete needs to be

compatible with the method of construction to ensurethat full-depth compaction of the concrete can be

achieved.

Slump is used as a measure of workability. The

method of construction influences the slump required.

As a guide, the lowest slump consistent with adequate

workability should be used. For fixed-form paving with

manually operated vibratory equipment, slump values

are in the range 50 to 60 mm. For slip-form

construction with no side forms, slump values in the

range of 30 to 50 mm are typical.

8.7 CHEMICAL ADMIXTURES

Chemical admixtures are commonly used to modify

the properties of concrete, making it more suitable for

a particular purpose. Chemical admixtures should not

be regarded as a substitute for, but rather part of

good mix design and good concreting practice.

8.8 CONSTRUCTION PRACTICES

The placing, compacting, finishing and curing of

concrete have a major influence on its strength anddurability.

Concrete should be thoroughly compacted,

particularly around reinforcement and in corners of

forms. If concrete is not adequately compacted (by

surface and/or immersion vibrators) air voids in the

hardened concrete will result in a pavement of less

than optimum strength, and possibly in corrosion of

reinforcement and/or spalling.

The strength of concrete falls rapidly as the percentage

of air voids increases. For example, a 2% reduction

below maximum density resulting from poor compaction,

lowers the strength by about 10%. If concrete

contains 5% of air voids, its strength is likely to be

about 30% below that of fully compacted concrete7.

When placing concrete during high evaporative

conditions such as hot, dry and/or windy weather, the

finishing operation will require additional attention.

These conditions will reduce the time available for the

sfinishing operation and may also result in plastic

cracking due to the surface of the concrete drying

rapidly, generally before the full depth of the concrete

has had time to take its initial set. More information

21


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about evaporative conditions can be found in

Chapter 12 of the Guide to Concrete Construction6.

Loss of surface moisture due to evaporation can beminimised by the erection of sunshades or windbreaks.

More particularly with concrete pavements, the

application of an evaporation retardant to the surface

of the concrete is required immediately after the initial

screeding has been completed. The evaporation

retardant forms a thin film over the surface of the wet

concrete that reduces evaporation by up to 80% in

windy conditions without interfering with subsequent

finishing.

The continued presence of moisture for hydration of

the cement binder, especially in the first few daysafter concrete is placed, is essential for the

development of concrete strength and durability. If a

concrete pavement is not properly cured, the surface

will be weak and since it is subject to abrasion

therefore prone to wear. Concrete pavements are

relatively thin and have a high surface to volume ratio.

Under most site conditions the potential for moisture

loss immediately after placing is therefore quite high.

Moisture loss must be controlled by appropriate curing.

Methods of curing can be split into two groups:

Those that offset water loss, eg fine continuouswater spraying;

Those that seal the surface and thus control water

loss from the concrete, eg covering with plastic

sheeting or coating the concrete with a membrane

curing compound, such as water-based or wax

emulsion which can be brushed, sprayed or

rolled onto the surface of the pavement.

The relative performance of curing methods in

controlling moisture loss from concrete is shown in

Figure 8.1. AS 379922 sets out the characteristics and

requirements for liquid membrane-forming curingcompounds for concrete. Water-based curing

compounds are commonly used with concrete

pavements as they are considered to be efficient and

user friendly.

The minimum periods for which concrete must be

cured are set out in AS 360018. These vary with the

strength of the concrete and the conditions to which it

is exposed. Plain or reinforced concrete pavements in

contact with non-aggressive soils are to be initially

cured continuously for at least three days under

ambient conditions or at least seven days in tropical,industrial and near coastal environments.

Unlike other paving materials, the rate of strength

gain in concrete is time-dependent and it must be

protected from traffic until adequate strength has

been achieved to resist the imposed load stresses.

The appropriate time for opening the pavement to

traffic will be dependent on the anticipated traffic

(both volume and loads need to be considered), the

strength grade of the concrete, and the elapsed time

since placing.

As a general rule, it is suggested that the pavement

should not be trafficked until it has gained 60% of its

specified 28-day pavement-design strength. This is

usually about seven days after placing. If earlier

trafficking is necessary then there is a variety of

techniques that can be used, solely or in combination,

to attain the necessary strength in the required time.

These techniques include using a higher strength of

concrete, accelerators, thermal curing, heated mixing

water, vacuum dewatering, etc. Alternatively the

stress in the pavement can be reduced by

temporarily covering with steel plates or planks. With

these techniques pavements can be opened within

12 to 24 hours or even sooner.

22

Waxemulsion

Hydrocarbonresin

Acrylicemulsion

Water-based

PVAemulsion

100

Efficiency Index (%)

AS 3799 requirements( 90% after 72 hours)

90 80 70 60 50 40 30 20 10 0

Figure 8.1 Comparative efficiency of curing

compounds


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9.1 GENERAL

The selection of concrete pavement type and overall

configuration for a given project is a decision for the

designer. Some of the factors that might influence

such a decision are:

size of the project;

availability of the appropriate equipment and

skilled operators;

effects of delays to street users;

ease of site access when performing joint filling

and other maintenance operations.

9.2 DESIGN CONCEPT

The design procedure for thickness design is based

on the same method as that used in Austroads

pavement design guide2. This method is based on

the procedure developed by the PCA23. It involves

the assessment of the:

predicted traffic volume and composition over the

design period;

strength of the subgrade;

strength of the concrete to be used in the

pavement.

This manual gives pavement thicknesses for plain

and reinforced concrete pavements.

9.3 FACTORS USED

Subgrade strengthThe subgrade strength

should be assessed in terms of CBR. Details of

subgrade support and preparation are discussed

in Section 6 Subgrades.

Concrete strengthThe factors affecting concrete

strength and durability are discussed in Section 8

Concrete.

The thickness design tables given in this guide

are based on concrete having a 28-day designcharacteristic flexural strength of 3.5 or 4.25 MPa.

Design Traffic The evaluation of design traffic in

CVAG is discussed in Section 5.3 Traffic Estimation.

9.4 CONCRETE SHOULDERS

The provision of a concrete shoulder with the

pavement improves its performance. The design

procedure takes this into account, enabling the

adoption of a reduced base thickness. To permit this,

a concrete shoulder should have at least the same

strength as the concrete base and is defined as:

a keyed and tied shoulder with a minimum width

of 1.5 m from the edge of the trafficked lane; or

a 600-mm integrally cast widening of a trafficked

lane (this may include integral channel or kerb

and channel).

Note: extruded kerb and channel, even if well tied to

the base, is not considered equivalent to a shoulder

for design purposes due to its lower strength.

However, a compacted slip-formed kerb and channel

can be considered as a shoulder.

The adoption of the with-shoulder case can also be

justified if the majority of heavy vehicles travel at least

600 mm from the pavement edge (see Matthews and

Mulholland24

). This may occur in car parking areas orstreets that provide for, or at least expect, roadside

parking. Tables 9.1 to 9.4 cover thicknesses of

pavements with or without concrete shoulders.

9.5 DETERMINATION OF BASE

THICKNESS

The full procedure for the determination of the base

thickness is detailed in Austroads pavement design

guide2.

Concrete base thicknesses have been developed

using the full design procedure. For simplification,

Tables 9.1 to 9.4 indicate the minimum thickness

produced by each load spectrum for the particular

load condition for design lives of 20 and 40 years.

9.6 STEEL REINFORCEMENT

9.6.1 General

The role of steel reinforcement in a concrete pavement

is not to prevent cracking, but to control drying

shrinkage cracking that may occur in slabs longer

than those permitted in unreinforced pavements. Theuse of steel reinforcement does not increase the load

23

09 Thickness Design


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24

TABLE 9.1 Concrete base thickness (mm) for Subgrade CBR 2%

CBR 2% NO SHOULDER WITH SHOULDER

Concrete flexural strength (MPa) Concrete flexural strength (MPa)

3.5 4.25 3.5 4.25

Design life (yr) Design life (yr) Design life (yr) Design life (yr)

Street type 20 40 20 40 20 40 20 40

Minor single-lane 190 200 170 170 160 170 140 140

two-way 190 200 170 170 160 170 140 150

Local access no buses 200 210 170 190 170 180 150 150

with buses 210 220 190 190 180 190 160 160Industrial area 210 210 180 180 170 180 150 150

Collector no buses 230 240 200 200 190 200 170 170

with buses 240 250 210 210 200 210 180 180



Concrete flexural strength (MPa) Concrete flexural strength (MPa)3.5 4.25 3.5 4.25


Street type 20 40 20 40 20 40 20 40


two-way 180 180 150 160 150 150 130 130


with buses 190 200 170 180 170 170 150 150

Industrial area 180 190 160 170 160 160 140 140


with buses 210 220 190 190 180 190 160 160


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25



Concrete flexural strength (MPa) Concrete flexural strength (MPa)

3.5 4.25 3.5 4.25


Street type 20 40 20 40 20 40 20 40


two-way 170 170 150 150 140 150 130 130


with buses 190 190 170 170 160 170 140 150industrial area 180 180 160 170 150 160 130 140


with buses 200 210 180 180 180 180 150 160



Concrete flexural strength (MPa) Concrete flexural strength (MPa)3.5 4.25 3.5 4.25


Street type 20 40 20 40 20 40 20 40


two-way 160 170 140 150 140 140 120 130


with buses 180 180 160 160 160 160 140 140

Industrial area 170 180 150 160 150 160 130 130


with buses 200 200 180 180 170 180 150 150


27/50

capacity of the pavement and is independent of

thickness design. Reduction in thickness is not

permitted when pavements are reinforced.

9.6.2 Reinforcement Design

Table 9.5 provides typical steel reinforcement

requirements for lightly trafficked residential streets

and for slab lengths less than 15 metres (maximum

slab length recommended).

9.6.3 Special Requirements for Unreinforced

Pavements

In unreinforced pavements, reinforcement of certain

slabs is recommended to control or minimise the

effects of cracking. These include slabs:

irregular in shape, or not square or near square

(ie a slab with a width:length ratio exceeding

1:1.25);

opposite a joint, ie mismatched joint (reinforce the

full slab);

containing pits or access holes (either internally, on

one edge or in a corner wholly within the slab).

For such slabs in pavements up to 230 mm thick, the

reinforcement required is SL62 Fabric. Details of joint

layout are shown in Section 10.6 Joint Layout.

9.6.4 Detailing of Steel Reinforcement

In order to perform as intended, the steel reinforcement

should be:

in the form of a single sheet located in the upper

half of the pavement base, subject to a minimum

top cover of 40 mm for pavements less than

150 mm thick and 50 mm for pavements greater

than or equal to 150 mm thick;

terminated 75 to 80 mm from transverse

contraction joints and isolation joints, and 40 to

80 mm from longitudinal warping joints where

joints are induced by sawing. Reinforcement may

continue over the joint location, however greater

care is required in the timing of the saw cut;

located above dowel bars or tie bars;

lapped so that the two outermost wires of one

sheet of fabric overlap the outermost wire of the

sheet being lapped (lapped portions should be

tied with wire at a maximum spacing of 500 mm);

handled so that sheets are free from undue

distortions or kinks;

free from material which may affect bond with the

concrete (a light coating of rust on the

reinforcement will not impair its performance);

supported on bar chairs in a regular grid not

exceeding 1 m (it should neither be stamped

down into the concrete nor laid on the ground

and raised into the concrete);

secured to the subbase in such a way as to resist

displacement during concrete placing.

9.6.5 Continuously Reinforced Concrete

Pavements

Continuously reinforced concrete pavements require a

more complex reinforcement design procedure than

that used for jointed pavements. For further information

on this procedure refer to Austroads pavements

design guide2.

9.6.6 Steel Fibre Reinforced Pavements

The use of steel fibre reinforced concrete is

appropriate to control cracking in irregular shaped

slabs. This type of pavement is often used at

roundabouts and bus bays.

Steel fibres are generally between 15 and 50 mm in

length with either an enlarged end that acts as

anchorage and/or crimping to improve bond. Typically,

fibres 15 to 50 mm in length are added to the concrete

at a rate of approximately 75 to 45 kg/m3 respectively

(referred to as 'fibre loading'). The steel fibre

suppliers recommendations on concrete strengths,

thickness and joint design should be obtained. For

more information refer to Fibres in Concrete25.

26

TABLE 9.5 Steel reinforcement for slabs up to

15 metres long

Concrete base Steel reinforcing fabric

thickness (mm) (to AS/NZS 4671)

125 SL62

150 SL72

175 SL82

200 SL82

225 SL92

250 SL92


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10.1 GENERAL

As has been previously stated in Section 4.6 Joints,

the objectives of joint design are to develop a jointing

system which will control transverse and longitudinal

cracking, and provide enough load transfer across

joints so that the pavement will have adequate riding

qualities over its service life. Section 4.6 also provides

definitions of the three types of joints that may be

required in concrete pavements contraction,

construction and isolation.

When contraction joints are spaced and sealed as

recommended, expansion joints will not be required in

residential street pavements. When joints are not

sealed, some expansion joints will be required.

Unsealed, tied, longitudinal, contraction joints should

be kept to 3 mm or less in width to minimise the risk

of spalling.

10.2 CONTRACTION JOINTS

10.2.1 Classification

When viewed in the direction of paving, contraction

joints fall into two categories, namely transverse and

longitudinal as shown in Figure 10.1, commonly

known as; transverse contraction joints and

longitudinal warping joints.

Both are constructed either by early-age powersawing or by placing an insert in the fresh concrete.

This locally reduces the concrete thickness, inducing

cracking at these locations whilst limiting it elsewhere.

10.2.2 Transverse Contraction Joints

Transverse contraction joints should:

provide for adequate load transfer across the

joint;

permit longitudinal movement at the joint;

incorporate a reservoir for a joint sealant.

The recommended detailing of transverse contraction

joints is shown in Figure 10.2. Note that the specified

depth of the saw cut or insert must be at least one-

quarter, and not more than one-third, the concrete

thickness to ensure that cracking will be induced at

these locations and that there is adequate load

transfer across the joint by the action of aggregate

interlock. The depth of the saw cut may be reduced

when early saw cutting of plastic concrete is made

using purpose designed equipment such as a Soff-cut

saw. In this latter case, the depth of the saw cut

should be to the manufacturers recommendations.

27

10 Joints

TiedLONGITUDINAL JOINT

Longitudinal joint

Jointedunreinforcedpavement

Jointedreinforcedpavement

Transverse joints

TRANSVERSE CONTRACTION JOINTS

Undowelled Dowelled

Figure 10.1 Contraction joints

UNDOWELLED JOINT jointed unreinforced pavements

DOWELLED JOINT jointed reinforced pavements

t

0.25t

0.5L + 25

0.5L

Bond-breakingcompound

Dowel(length, L)

t

50 minimum

75 75

Induced crack

Sealant reservoirand sealant

0.5t

Figure 10.2Transverse contraction joint details


29/50

The joint spacings shown in Table 10.1 are such as toensure load transfer by aggregate interlock at the

fractured joint face. To supplement load transfer in

heavily trafficked pavements, a bound subbase may

be used (see Section 7.4).

For reinforced pavements, transverse contraction

joints can be spaced at suitable intervals up to a

recommended maximum of 15 metres. For practical

and economic reasons, a slab length of 12 metres is

typically specified. Since these joints will open and

close to the extent that load transfer by aggregate

interlock will not be effective, smooth steel dowels areinstalled to provide the necessary load-transfer

capacity. A joint of this type will also be required at

the connection of a jointed reinforced pavement to a

jointed unreinforced pavement.

To permit joint movement, the dowels must be:

sawn not cropped at least on one end;

straight, smooth and free of burrs;

effectively de-bonded over at least half their

length;

placed orthogonal to the joint direction andparallel to the pavement surface.

Proper field supervision of the placing of the dowels is

crucial to good performance as failure to meet all of

these requirements can cause the joint to 'lock',

leading to distress at the joint and spalling. Dowels

should be Grade 250R steel bars, 450 mm long and

placed at 300-mm centres. Dowel diameters are

shown in Table 10.2.

Dowels should be placed in assemblies and firmly

secured to the subbase to avoid disturbance during

concrete placing. The dowel-assembly support frame

should not pass through the joint. The insertion of

dowels during the placing of concrete is not

acceptable. A typical dowel assembly is shown in

Figure 10.3.

10.2.3 Longitudinal Warping Joints

Longitudinal joints are provided to control longitudinal

cracking which can occur after construction as a

result of slab warping combined with traffic loading.

The detail of this type of joint is shown in Figure 10.4.

Note that the specified depth of the saw cut or insert

must be at least one-third the concrete thickness to

ensure that cracking will be induced at this location.

These joints can also serve as construction joints.

For unreinforced pavements, the intervals betweenlongitudinal joints should not exceed 1.25 times the

maximum transverse contraction joint spacing. For

reinforced pavements, the spacing should not exceed

5 metres, except in pavements with a uniform one-way

crossf

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